On 2019-07-15 18:15, buffstereo wrote:> On Tuesday, July 9, 2019 at
Post by Peter Wieck Post by Paul James
Does anyone here have any experience with using 171a in a
linestage. Thinking of using constant current.
Post by Peter Wieck
The 71A is a low-gain DHT that is valued and prized by the Vintage
Radio community. You in the Audio Community have multiple options for
this purpose that do not suck resources from your cousin. Who have, too
often, no viable alternatives.
Well the antique radio crowd has often had to re-wind transformers and
do other things to restore an old radio to "original" as much as possible.
So here's a thought: what if it were possible to actually RE-BUILD one
of those old tubes? It would require all of the right stuff, vacuum
gear, glass blowing equipment, and some way to make all of the various
electrode components according to the original spec. You might even
need 'exotic metals', dangerous chemicals, nitrogen purges to get rid of
O2 and H2O vapor, and so on.
There was once a popularity of picture tube re-building "kits", ones
I've heard about online anyway, where you'd get a set of popular
electron guns to put into 'dud' tubes. I suppose they could also be
re-phosphored somehow, not sure how well THAT would work. But the
skills and equipment to do that sort of thing isn't all that available
any more, and I'm sure there are *RIDICULOUS* "environmental"
stupid-laws that get in the way of doing that sort of thing on a
commercial basis. Quite frankly, you could NEVER get zoning for that
sort of thing inside of a city. This is probably why most tubes are now
made in eastern Europe [where they even use leaded gasoline still, from
what I've heard], and in Ruswia, and in China, and other places where
they seem to NOT have a problem with polluting everything around them.
[I wouldn't want to pollute everything, just design the systems
carefully so that the hazardous material can be properly disposed of,
and NOT "ban it outright" in a knee-jerk overreaction as is the case all
too often, especially in places like Cali-Fornicate-You]
In any case, I've seen stuff online about home-made tubes. To do these
right you need the original specs and drawings so you can replicate the
parts and the distances properly. Then you'd have to be able to curve
trace them [to verify the specs match] and somehow recycle the fallouts
so you aren't tossing a lot of valuable (possibly rare, possibly
and it would be VERY labor intensive, unless there's some kind of
robotic manufacturing process that could do customized tube re-making.
So things I think would be needed that could re-use components:
a) replacement heaters
b) cathode re-coating
c) insulator disk replacement
d) socket replacement [probably have to because of the glass seals
around the pins, you'd have to re-do all of this probably]
e) 'getter material' and that silvery spot that consists of sodium or
some other oxygen scavenging metal
Other than that, if the grids aren't damaged, and the cathode needs
re-coating but is otherwise ok, then a replacement filament plus re-coat
cathode and the tube should be like new again. Well, after getting the
vacuum and getter stuff right, anyway.
[there'dd be no money in it, and it'd have to be a kind of "labor of
love" hobby by people who want to preserve antique radios and tube
electronics in general]
My $.10 worth